In the case of a door opening/closing apparatus disclosed in Patent Document 1 as an example of prior art document information relating to the door opening/closing apparatus of the above-noted type, as a metallic coating for providing metallic lustrous aesthetic property to a cover to be attached to a main body of the door handle, there is effected a spray coating of a coating material containing, as major components thereof, fine metal particles of aluminum or aluminum alloy and acrylic resin. In doing this, care is taken not to form discontinuous portions of the fine metallic particles wherein the particles are present in discontinuous manner. This is done by positively reducing the thickness of the coating film to from 0.1 to 40 μm. The document reports that loss in antenna output due to the metallic coating was restricted as the result of the above arrangement.
However, with the door opening/closing apparatus disclosed in Patent Document 1, it is difficult to control such that the film thickness of the coating film be uniform. Consequently, there would occur uneven distribution of the fine metal particles, thus inviting the risk that the level of change in the electrostatic capacitance due to a touch by a user's hand varies significantly depending on the position of the hand relative to the door handle. Further, in this known coating arrangement, the fine metal particles are distributed in the acrylic resin as the coating film. Hence, it is difficult to obtain good luster performance equivalent or comparable to that of a metal plating.
On the other hand, according to a further door opening/closing apparatus disclosed in Patent Document 2 which is another prior-art document, in an attempt to overcome the above-described problems present in the technique of Patent Document 1 and to ensure reduction in the antenna output loss as well as stability of communication while retaining metallic luster as substantially good as that of plating, a metal thin film is formed by the sputtering technique on the outer surface of the door handle. The metal cited as an example of a target of sputtering in Patent Document 2 is Cr.